Field of the Invention
The present invention relates to a method of producing micromechanical structures that are formed on a base body and are protected from damage by a covering body.
Micromechanical structures are used, for example, as acceleration sensors for triggering airbags. The micromechanical structures in this case contain self-supporting parts, such as diaphragms or spring beams or the like, which bend when exposed to acceleration. On the basis of the bending, a value for the acceleration is determined.
Micromechanical structures are disposed, for example, on the surface of a base body and are protected from environmental influences, such as mechanical or chemical destruction, by a covering body.
Methods of producing micromechanical structures are specified, for example, in references by Sven Michaelis and Hans-Jörg Timme, titled “Acceleration Threshold Switches from an Additive Electroplating MEMS Process”, Eurosensors XIII, The 13th European Conference on Solid State Transducers, Sep. 12-15, 1999, The Hague, The Netherlands; by M. Wycisk, T. Tönnesen and J. Binder, S. Michaelis and H. J. Timme, titled “Low Cost Post-CMOS Integration of Electroplated Microstructures for Inertial Sensing”, and by M. Wycisk and J. Binder, S. Michaelis and H. J. Timme, titled “New Sensor On-Chip Technology for Micromechanical Acceleration Threshold Switches”.
A method of covering micromechanical structures is described, for example, in a reference by Sven Michaelis, Hans-Jörg Timme, Michael Wycisk, Josef Binder, titled “Additive Electroplating Technology as a Post-CMOS Process for the Production of MEMS-Acceleration Threshold Switches for Transportation Applications”. Used in this case is a specially prepared covering body with cavities on its underside, in which the micromechanical structures that are disposed on the base body are protected. Also disposed in the covering body are through-holes, in which the contact pads of the base body are accessible after the base body and the covering body have been joined together. If the holes were not present, it would not be possible for electrical contacts to be established for the structure.
The holes in the covering body make it liable to break and susceptible to cracks. This in turn leads to low yields and high costs. In addition, the production of the holes is a laborious etching process which takes over six hours and is therefore costly.
A further method of covering micromechanical structures and exposing the contact pads is to use sawing methods, in which large pieces of the covering body are sawn out and swept away in the flushing operation accompanying sawing. The sweeping-away of the large pieces entails a high risk of damage to the structures and also leads to breakages of the saw blade.